This project represents an on-going study of the mechanical properties of the normal and diseased heart. It is concerned with an evaluation of systolic indices of ventricular performance, derived in terms of both muscle function and pump function, as well as an examination of the diastolic properties of the left ventricle in the normal dog heart and the normal and diseased human heart. Parallel studies of isolated mammalian heart muscle are being carried out with particular attention paid to the effect of hypoxia and reoxygenation upon performance of heart muscle. In addition, an analysis of the effects of regional ischemia and reoxygenation of ischemic myocardium upon the electrophysiological and mechanical behavior of the intact dog heart is under investigation. These studies include measurements of ventricular fibrillation thresholds, dispersion of the refractory period, analysis of spontaneous ventricular arrhythmias and measurements of segment tension duration. Broadly speaking, the project is concerned with the underlying mechanisms of ventricular hypertrophy and myocardial failure and a study of mechanisms of sudden death in experimental regional myocardial ischemia.